Abstract
The proteasome is a 2.5-MDa multisubunit protease complex that degrades polyubiquitylated proteins. Although its functions and structure have been extensively characterized, little is known about its molecular dynamics in living cells. By using fluorescence correlation spectrometry, a method for quantitative imaging, we determined the absolute concentration, dynamics, and complex formation of the proteasome in living cells. The proteasome is a highly mobile complex and almost all proteasome subunits are stably incorporated into the proteasomes. We also revealed that the proteasome completes its assembly process in the cytoplasm and translocates into the nucleus as a holoenzyme.
